continued from: Starlit Sky: 5. Taurus and Pleiades
Hope you all saw Orion and Taurus constellations in the night sky. Using the Orion constellation, we will go on and identify more stars and constellations. Let’s get right into it straightaway.
By extending the belt of the hunter westwards, we had identified the Taurus constellation. Now lets extend the belt east wards now.
Now we have reached a very very bright star that shines with white light. That is Sirius.
Sirius is the brightest star that we can see from Earth after Sun. It is also the nearest to the Earth being only 8.6 lightyears away. It is called Mrigavyadha Rudra in Sanskrit. The apparent magnitude of Sirius is -1.46.
What looks like a single star with naked eye is actually a binary star. The faint binary star that is associated with Sirius is actually a white dwarf and is called Sirius B. It can be seen with a binoculars. These two orbit each other every 50 years. They were last closest together in 1993 and they will be farthest next 2020. Sirius B is 10,000 times fainter than Sirius A to an observer on Earth. Sirius A is twice as big as our Sun but is 25 times more luminous than Sun.
Sirius formed an important part of the daily life of our ancestors. Its appearance in the eastern sky along with the Sun’s rising (called the helical rising) in the Northern hemisphere marked the annual flooding of the Nile river. It also marked the summer days for Greeks. They called them the “dog days”. The appearance of this star in the Southern Hemisphere was the indication of the winter there.
It was used as a navigation tool in the vast Pacific Ocean by the sailors of yore.
Did you know? Sirius is moving toward the Earth slowly, and it will be more bright in about 60,000 years from now, then again it will move farther away. But still it will continue to hold the title of the brightest star in the night sky. You know, I always wonder about the ways in which man has been able to calculate about all the paths and timelines of the celestial bodies. What a wonder is God’s creation and the biggest wonder is the human brain! Don’t you agree?
Sirius A and Sirius B form a binary star system that are about 200 to 300 million years old. Sirius B was bigger than Sirius A. It consumed all its energy and became a white dwarf. If you take a spoonful the star material from Sirius B, it will weigh tons of kilograms! Can you imagine!! Wow!!!
Binary star: A binary star system is one where two stars go around each other. If more than 2 stars orbit around each other it is called a multiple star system.
White dwarf: A star’s energy comes from fusion of the nuclei of hydrogen atoms forming helium. When all the fuel (hydrogen atoms) is over, that is there are no more material to be fused, then the star has no source of energy. And so it cannor support itself against the gravitational collapse. So the star collapses on itself and all the material gets compressed and pulled inwards due to extreme gravity. Then it becomes a white dwarf. Its mass will be very very high though its volume will be relatively small. When it forms, a white dwarf will be hot, but since it has no more energy it will cool down considerably by radiating its light. Gradually there will be no more light to emit and it will turn into a black dwarf. Turning into a black dwarf takes so much time, that there are no black dwarfs yet in the universe. Eventually all stars will become black dwarfs and that will mark the end of time.
Supergiant: Supergiants are among the most massive and luminous stars. Certain stars in their evolution, reach this stage. When a massive star reaches the end of its supply of hydrogen for fusion, it continues fusing to form the heavier elements. For example 2 helium nuclei will fuse and form beryllium, or one helium and one hydrogen will fuse to become lithium etc and so on. Thus all the elements of higher atomic numbers are formed. Once iron is formed in the core, the core collapses and the star explodes to form a supernova. This supernova then cools to give birth to a new star. And then the cycle continues.
Sirius is a part of the constellation called Canis Major, or the Greater Dog. That is why Sirius is also called the Dog star. Canis Major has about 12 stars. Put together, they give an impression of a dog. Sirius forms the pendant in the neck of the dog. We imagine this dog belongs to the hunter as he hunts the bull (Taurus).
Besides Sirius, some of the other stars of this constellation are:
- Epsilon Canis Majoris or Adhara, with a brighness of 1.5. It is next in brightness to Sirius. It forms the thigh of the hind leg of the dog.
- Delta Canis Majoris or Wesen, forming the hip of the dog. This is a yellow-white supergiant with brightness of 1.8
- Beta Canis Majoris or Mirzam, the front leg of the dog with brightness of 2.0.
- Eta Canis Majoris or Aludra is the tail of the dog. It is a super giant too with brightness of 2.4
M41 or Messier 41:
About 4 degrees south of Sirius shine a bunch of bright stars. That is M41 (See fig below for location). It is not one star but is an open cluster of about 100 stars, some of them being red giants. It is about 1300 light years away and has a diameter of almost 26 to 26 light years.
M41 also is a part of the Canis Major.
Look up at the sky and find all these stars. Next week we will explore more and find Canis Minor.
to be continued…………………